/*                   _   _ _ __                               *\
**     ________ ___ | | | | '_ \   scaup - Scala up!          **
**    / __/ __// _ || | | | |_) |  (c) 2008, Normen Mueller   **
**  __\ \/ /__/ __ || |_| | .__/   http://kwarc.info.nmueller **
** /____/\___/_/ |_/ \__,_|_|                                 **
**                                                            **
\*                                                            */
  
// $Id: SourceReader.scala 9 2008-05-24 12:12:30Z normen.mueller $

/* This class has its origin at: scala.tools.nsc.io.SourceReader */

package scaup.io.fs

import java.io.{File, FileInputStream, InputStream, IOException}
import java.nio.{ByteBuffer, CharBuffer}
import java.nio.channels.{FileChannel, ReadableByteChannel, Channels}
import java.nio.charset.{CharsetDecoder, CoderResult}

/** This class implements methods to read and decode source files. */
class SourceReader(decoder: CharsetDecoder) {

  import SourceReader.{decode, flush}

  /** The input byte buffer (small enough to fit in cache) */
  private val bytes: ByteBuffer = ByteBuffer.allocate(0x4000)

  /** The output character buffer */
  private var chars: CharBuffer = CharBuffer.allocate(0x4000)

  private def reportEncodingError(filename:String) = {
    Console println "IO error while decoding "+filename+" with "+decoder.charset();
  }

  /** Reads the file with the specified name. */
  def read(filename: String): Array[Char]= read(new File(filename))

  /** Reads the specified file. */
  def read(file: File): Array[Char] = {
    val c = new FileInputStream(file).getChannel
    try {
      read(c)
    } catch {
      case e:Exception =>
        reportEncodingError(file.toString())
        new Array[Char](0)
    } finally {
      c.close()
    }
  }

  /** Reads the specified file.
  @param file ...
  @return     ... */
  def read(file: AbstractFile): Array[Char] = {
    file match {
      case p:PlainFile =>
        read(p.file)                                                     // bq: (!!!)
      case z:ZipArchive#FileEntry => 
        val c = Channels.newChannel(z.getArchive.getInputStream(z.entry))
        read(c)
      case _ =>
        throw new IOException(file.toString()+" is neither plain file nor ZipArchive#FileEntry")
    }
    /*
    val decoder: CharsetDecoder = this.decoder.reset();
    val bytes: ByteBuffer = ByteBuffer.wrap(file.read);
    val chars: CharBuffer = this.chars; chars.clear();
    try {
      terminate(flush(decoder, decode(decoder, bytes, chars, true)));
    } catch {
      case e:Exception => 
        reportEncodingError(file.toString())
        new Array[Char](0)
    }
    */
  }

  /** Reads the specified byte channel. */
  protected def read(input: ReadableByteChannel): Array[Char] = {
    val decoder: CharsetDecoder = this.decoder.reset()
    val bytes: ByteBuffer = this.bytes; bytes.clear()
    var chars: CharBuffer = this.chars; chars.clear()
    var endOfInput: Boolean = false
    while (!endOfInput ) {
      endOfInput = input.read(bytes) < 0
      bytes.flip()
      chars = decode(decoder, bytes, chars, endOfInput)
    }
    terminate(flush(decoder, chars))
  }

  /** Sets the specified char buffer as the new output buffer and reads and returns its content. */
  private def terminate(chars: CharBuffer): Array[Char] = {
    val result = new Array[Char](chars.length())
    chars.get(result)
    this.chars = chars
    result
  }

}

object SourceReader {

  /** Decodes the content of the specified byte buffer with the specified decoder into the specified char buffer, allocating bigger ones if necessary, then compacts the byte
  buffer and returns the last allocated char buffer. The "endOfInput" argument indicates whether the byte buffer contains the last chunk of the input file. */
  def decode(decoder: CharsetDecoder, bytes: ByteBuffer, chars: CharBuffer, endOfInput: Boolean): CharBuffer = {
    val result: CoderResult = decoder.decode(bytes, chars, endOfInput)
    if (result.isUnderflow()) {
      bytes.compact()
      chars
    } else {
      if (result.isError()) throw new IOException(result.toString())
      assert(result.isOverflow())
      decode(decoder, bytes, increaseCapacity(chars), endOfInput)
    }
  }

  /** Flushes the specified decoder into the specified char buffer, allocating bigger ones if necessary and then flips and returns the last allocated char buffer. */
  def flush(decoder: CharsetDecoder, chars: CharBuffer): CharBuffer = {
    val result: CoderResult = decoder.flush(chars)
    if (result.isUnderflow()) {
      chars.flip()
      chars
    } else {
      if (result.isError()) throw new IOException(result.toString())
      assert(result.isOverflow())
      flush(decoder, increaseCapacity(chars))
    }
  }

  /** Flips the specified buffer and returns a new one with the same content but with an increased capacity. */
  private def increaseCapacity(buffer: CharBuffer): CharBuffer = {
    buffer.flip()
    val capacity = 2 * buffer.capacity()
    CharBuffer.allocate(capacity).put(buffer)
  }

}
